A token is specific to a particular UserID and AppID. The site/country are irrelevant.
There are many operations that are only possible with a token created for a particular UserID. For example, only the seller can retrieve the buyer's shipping address.
I'm writting an app, which lets auction creator (some seller) to fetch her bidders contact information (phone, address, email). Currently I only managed to get email via GetUser() API call (when ItemID provided in request). How can I get more detailed info ??